The invention relates to a hydropneumatic vibration damper of variable damping force having a cylinder and piston arrangement with an electromagnetically actuable valve.
DE 36 31 714 A1 discloses a hydropneumatic vibration damper of variable damping force, which has an electromagnetically adjustable bypass valve for the damping valve assigned to tensile damping and located in the piston and has a further electromagnetically adjustable bypass valve for the bottom valve taking effect in the event of compressive damping. Thus, although the electromagnet for the bypass valve assigned to the bottom valve is located underneath the bottom valve, the associated bypass duct nevertheless passes through the bottom valve body centrally and, moreover, a damping valve preceding the bypass valve projects into the lower working space of the vibration damper. In the case of such a design, the electromagnet located underneath the bottom valve can change only the damping force in the compressive stage, while a further electromagnetic adjusting device in the region of the piston is required in order to change the damping force in the tensile stage. Accordingly, because of the multiplicity of components which are necessary, such a vibration damper of variable damping force involves a high outlay in terms of construction and is costly to produce and assemble. Furthermore, such an arrangement of the bypass valves necessitates a relatively large construction space in the axial direction.
An electromagnet arranged between the container bottom and the bottom valve is also shown in DE 38 07 913 C1, the individual parts of the valve device and a tube receiving the valve armature being integral parts of the cylinder. Only the coil of the electromagnet is installed between the structural unit connected to the cylinder and a return pot, this return pot, seated positively and fixedly in terms of rotation in the container bottom, serving essentially for installing the coil of the electromagnet in the correct position.
In another vibration damper of variable damping force according to EP 0 517 875 B1, an electromagnetically variable damping valve assigned to compressive damping is arranged in the bottom valve, while the damping valve for tensile damping is seated in the piston and cooperates with a regulating mechanism having a central tube which passes centrally through the bottom valve and which is sealingly guided axially movably in a hollow piston rod. The design of a vibration damper of this type is highly complicated and costly, since each damping direction is assigned a separate damping valve and, moreover, the central tube has to be guided in the piston rod with great accuracy and sealed off.
The object of the present invention is to provide a hydropneumatic vibration damper of variable damping force, which has a simple design and can be produced cost-effectively, allows it to be set to the required damping forces without difficulty and occupies only a small amount of construction space.